This invention relates generally to a reliable an effective method for determining that and iontophoretic sampling system can provide a predicable response to a known concentration of an analyte of interest. The invention also relates to kits useful in the practice of the method of the present invention. In one embodiment, the analyte of interest is glucose.
A number of diagnostic tests are routinely performed on humans to evaluate the amount or existence of substances present in blood or other body fluids. These diagnostic tests typically rely on physiological fluid samples removed from a subject, either using a syringe or by pricking the skin. One particular diagnostic test entails self-monitoring of blood glucose levels by diabetics.
Diabetes is a major health concern, and treatment of the more severe form of the condition, Type I (insulin-dependent) diabetes, requires one or more insulin injections per day. Insulin controls utilization of glucose or sugar in the blood and prevents hyperglycemia which, if left uncorrected, can lead to ketosis. On the other hand, improper administration of insulin therapy can result in hypoglycemic episodes, which can cause coma and death. Hyperglycemia in diabetics has been correlated with several long-term effects of diabetes, such as heart disease, atherosclerosis, blindness, stroke, hypertension and kidney failure.
The value of frequent monitoring of blood glucose as a means to avoid or at least minimize the complications of Type I diabetes is well established. Patients with Type II (non-insulin-dependent) diabetes can also benefit from blood glucose monitoring in the control of their condition by way of diet and exercise.
Conventional blood glucose monitoring methods generally require the drawing of a blood sample (e.g., by fingerprick) for each test, and a determination of the glucose level using an instrument that reads glucose concentrations by electrochemical or calorimetric methods. Type I diabetics must obtain several fingerprick blood glucose measurements each day in order to maintain tight glycemic control. However, the pain and inconvenience associated with this blood sampling, along with the fear of hypoglycemia, has lead to poor patient compliance, despite strong evidence that tight control dramatically reduces long-term diabetic complications. In fact, these considerations can often lead to an abatement of the monitoring process by the diabetic.
Recently, various methods for determining the concentration of blood analytes without drawing blood have been developed. For example, U.S. Pat. No. 5,267,152 to Yang et al. describes a noninvasive technique of measuring blood glucose concentration using near-IR radiation diffuse-reflection laser spectroscopy. Similar near-IR spectrometric devices are also described in U.S. Pat. No. 5,086,229 to Rosenthal et al. and U.S. Pat. No. 4,975,581 to Robinson et al.
U.S. Pat. No. 5,139,023 to Stanley describes a transdermal blood glucose monitoring apparatus that relies on a permeability enhancer (e.g., a bile salt) to facilitate transdermal movement of glucose along a concentration gradient established between interstitial fluid and a receiving medium. U.S. Pat. No. 5,036,861 to Sembrowich describes a passive glucose monitor that collects perspiration through a skin patch, where a cholinergic agent is used to stimulate perspiration secretion from the eccrine sweat gland. Similar perspiration collection devices are described in U.S. Pat. No. 5,076,273 to Schoendorfer and U.S. Pat. No. 5,140,985 to Schroeder.
In addition, U.S. Pat. No. 5,279,543 to Glikfeld describes the use of iontophoresis to noninvasively sample a substance through skin into a receptacle on the skin surface. Glikfeld suggests that this sampling procedure can be coupled with a glucose-specific biosensor or glucose-specific electrodes in order to monitor blood glucose. Finally, International Publication No. WO 96/00110 to Tamada describes an iontophoretic apparatus for transdermal monitoring of a target substance, where an iontophoretic electrode is used to move an analyte into a collection reservoir and a biosensor is used to detect the target analyte present in the reservoir.
The present invention relates generally to a reliable and effective method for determining that an iontophoretic sampling system can provide a predictable response to a known concentration of an analyte of interest. In a preferred embodiment, the analyte of interest is glucose.
In one aspect, the invention includes a kit for testing the efficacy of an iontophoretic sampling system, where the iontophoretic sampling system has first and second surfaces and the first surface has a reservoir containing an ionically conductive medium, as well as, an enzyme capable of reacting with glucose to produce hydrogen peroxide. The kit comprises a cover and a container of glucose solution. The cover has a shape that encloses the reservoir. Further, the cover has a top surface, retaining sides, and a bottom surface where the bottom surface defines an opening such that when the bottom surface of the cover is in contact with the first surface of the iontophoretic sampling system the first surface completes a bottom for the cover and creates an enclosed space. The retaining sides are appropriately formed and may be, for example, be angular or curved. Further, the top of the cover defines an opening through which a solution can be introduced. In addition, the top of the cover may have a slit or other openings to allow for elimination of air bubbles. Such a slit is generally centrally located in the top of the cover. The kit also includes a container holding a stable solution of glucose, where the glucose solution has a volume sufficient to at least cover the ionically conductive medium, and preferably fill the enclosed space.
The cover of the present invention may be formed from materials including, but not limited to, polystyrene, polycarbonate, nylon, and polyester glycol.
The kit may further comprise an adhesive strip effective to seal the opening and the slit, where adhesion of the strip to the cover prevents glucose solution from leaking out.
One embodiment of the cover of the present invention is shown in FIGS. 5A, 5B, and 5C. FIG. 5C shows an exemplary flanged surface. Typically the first surface has an adhesive on it, however, the bottom surface of the cover may have an adhesive distributed on the surface.
The kit can include instructions for use.
In one embodiment of the invention, the glucose solution in the test kit has a concentration of 100 xcexcM. The solution may also contain a preservative. Such preservatives include, but are not limited to, sodium benzoate, methyl propyl isoparaben, sodium azide, and sodium nipagin. In a preferred embodiment, the preservative is sodium benzoate at 0.2% (w/w). An exemplary snap-top container for the glucose solution is shown in FIG. 6.
The present invention further includes, a method of testing an iontophoretic sampling system""s ability to determine the sensitivity of the sampling system relative to a concentration of glucose in a glucose solution, where the iontophoretic sampling system has first and second surfaces and the first surface has a reservoir containing an ionically conductive medium and an enzyme capable of reacting with glucose to produce hydrogen peroxide. The method includes, but is not necessarily limited to, the following steps:
(a) connecting the iontophoretic sampling system to appropriate sampling means;
(b) placing a cover, described above, on the iontophoretic sampling system,
(c) introducing a solution of glucose through the opening, where the glucose solution has a volume sufficient to at least cover said ionically conductive medium; and
(d) testing the iontophoretic sampling system""s sensitivity relative to a concentration of glucose in a glucose solution.
The invention also includes a method of testing an iontophoretic sampling system""s ability to determine the concentration of glucose in a glucose solution, following essentially the same steps as just described.
Further, in another aspect the invention includes a method of testing an iontophoretic sampling system""s ability to determine that an iontophoretic sampling system can provide a predictable response to a known concentration of glucose in a glucose solution. This method follows essentially the same step outlined above.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.